The invention relates to a semiconductor device comprising a coupling member. The coupling member couples an input light wave guide transporting a main light beam to secondary light wave guides each transporting a part of the intensity of this main light beam. The light wave guides are made of a semiconductor material. The coupling member is monolithically integrated with the wave guides on a semiconductor substrate.
The invention further relates to interferometer arrangements including such a coupling member and monolithically integrated therewith.
The invention finally relates to a method of manufacturing such a coupling member and interferometer arrangements
The invention may be used in, for example, the formation of modulators integrated on a substrate of gallium arsenide. The device modulates light sources, such as lasers, and is intended to operate at very high frequencies, i.e. of the order of 5 to 10 GHz. Such a device is suitable for use in the field of telecommunication. The invention may also be used in the formation of laser cavities, also integrated on gallium arsenide.
Such a coupling member between light wave guides is known from an article by P. Buchmann and A. J. N. Houghton entitled "Optical Y-Junctions and S-Bends Formed by Preferentially Etched Single-Mode RIB Waveguides In InP" (Electronics Letters, Sept. 16, 1982, Vol. 18, No. 19, pages 850-852). This article discloses a structure for separating light beams obtained by means of wave guides integrated on a substrate of indium and phosphide. The structure consists of a junction of the form of a Y. This structure is obtained by epitaxial growth of an n.sup.- type layer on an n.sup.+ substrate, and by a chemical attack of this layer through the openings of a mask.
After the chemical attack, the structure for separating beams appears in the n.sup.- type layer. The light wave guides have a rectangular cross-section and their external faces are formed so as to be as smooth as possible in order to improve the confinement of the light. The aperture angle of the branches of the junction is on the order of 0.9.degree..
This known member has numerous disadvantages. First, in spite of the small aperture of the branches of the Y junction, the losses due to the device design itself in addition to the losses due to the manufacturing method reach a very high value on the order of 4 dB. Furthermore, due to this small aperture, the branches of the junction necessarily have a great length, which can reach a value of 2 mm to assume that the light wave guides coupled to the branches are sufficiently remote from each other and do not interfere with each other. As a result, the members obtained by these structures have large dimensions.
Moreover, the main light wave guide of such a structure cannot admit several modes at a time, because the mode conversion provided by the Y-junction is not compatible with this operation.
Finally, when this structure is utilized for combining beams, if the beams entering at the branches of the Y are in phase, the light in fact emanates in an adequate manner through the main light wave guide. However, if the entering beams are in relative phase opposition, their recombination provides an optical mode of higher order--different from the fundamental mode. This higher order mode does not follow the main light wave guide and radiates into the substrate. In this case, the signal is lost. Consequently, such a structure cannot be utilized for forming, for example, an interferometer of the so-called "Michelson" type.